The present invention relates to a process for supplying a polyphase electric motor with electronic switching. It also relates to a supply circuit for practicing this process.
The supply of a polyphase motor with electronic switching from the monophase sector network generally uses a rectifier stage and a converter stage comprising electronic switches controlled from references and positional information from detectors, for supplying the different phases of this motor. The present invention relates more particularly but not exclusively to the case of variable reluctance motors with electronic switching supplied by a power converter.
It is to be noted that in present processes for supplying a motor with electronic switching, the current delivered by the supply is subject to disturbances which can be at multiple frequencies in the frequency sector. These disturbances can lead to exceeding values of current harmonics permitted by the standard CEI 61000-3-2. At present, this problem is solved by filtering the supply current so as to get rid of current harmonics greater than the frequency of the sector. A filter can for example be inserted, passive (based on L, C filters) or active (of the PFC type: xe2x80x9cPower Factor Correctionxe2x80x9d), between the rectifier stage and the converter stage. The addition of a PFC filter upstream of the converter stage leads to significant and prohibitive increase in the cost of the electronics, when the powers to be controlled exceed several hundreds of watts.
There is known from FR2 744 577 in the name of the present applicant, a process to supply a polyphase electric motor with variable reluctance and electronic switching from a source of rectified voltage, comprising for each phase, magnetization sequences during which the rectified voltage is applied to the phase, demagnification sequences during which the reverse of the rectified voltage is applied to the phase, a detection of disturbances affecting the current delivered by the rectified voltage source, and in response to such a detection, sequences of free wheeling during which the magnetic energy presently stored in at least one of the phases is substantially maintained in the latter.
However, it must be pointed out that the present supply processes are not completely satisfactory because they do not permit a wide latitude of operation of the motor or require costly filtering devices. In particular, there is not at present a satisfactory economic solution to provide an effective control of the current supply of the converter.
The object of the invention is to overcome these drawbacks by providing a process to supply an electronically switched motor, which will have greater flexibility of control than the present processes, to the end of satisfying the present constraints as to material for electromagnetic compatibility without having need to resort to active filtering devices such as PFC.
The above objects are achieved with a process to supply a polyphase electric motor with electronic switching from a voltage supply source, comprising:
passive electrical filtration downstream of the supply source to attenuate rapid fluctuations of the supply current delivered by said source,
conversion of the voltage supplied by the source to supply the phases of the motor, using an assembly of controllable switches having either a passive condition, or a blocked condition, each combination of conditions of the switches defining a conversion configuration,
a regulation of the supply current about a current reference, using alternation between two conversion configurations,
a determination of the mean supply current,
a sequencing of magnetization and demagnetization cycles of the phases of the motor, initiated by magnetization or demagnetization references of the phases, each cycle comprising a plurality of periods of sequencing within each of which said magnetization or demagnetization references do not change.
According to the invention, this process moreover uses, during at least one of the sequencing periods per cycle, several couples of conversion configurations such that the mean supply current respects as much as possible the reference current.
Thus, this supply process provides at least cost an effective control of the supply current, contributing to an optimization of the power factor and to the satisfaction of the constraints of electromagnetic compatibility. Moreover, the supply process according to the invention contributes to a substantial reduction of the acoustic noise generated by the motor thus supplied.
The sequencing period is here defined as a period of time in the course of which the orders or standards sent by a sequencer do not change. It is to be noted that within a period of sequencing, two couples of successive configurations can have an identical or equivalent configuration.
In a preferred embodiment of the process according to the invention, the latter comprises moreover a selection of a couple of configurations arranged to permit the introduction of two supply current values enclosing as nearly as possible the reference current and to take account of the magnetization or demagnetization references of the phases.
The supply process according to the invention can moreover preferably comprise a series of couples of configurations pre-defined as a function of the magnetization or demagnetization references.
There can also be provided a passage from one couple of configurations in use, to a following couple of configurations, when the couple of configurations in use no longer guarantees a production of two supply currents straddling the reference current.
It is advantageous to provide, at each start of a period, a determination of a first couple of configurations belonging to the series of couples pre-defined as a function of the last couple of active configurations of the preceding period, then a use of this first couple of configurations.
One of the configurations of the selected couple of configurations can for example comprise at least one free wheel condition.
In a particular embodiment of the supply process according to the invention, it can be provided that within a period of sequencing, two successive couples of configurations have an identical or equivalent configuration, producing substantially identical differences of potential in the motor phases.
In a first embodiment, the voltage source is a rectified AC voltage source and the current reference has a nearly sinusoidal rectified shape substantially in phase with the supply voltage.
In a second embodiment, the voltage source is a source of substantially constant voltage and the current reference is of substantially continuous shape.
According to another aspect of the invention, there is proposed a circuit to supply a polyphase motor with electronic switching from a source of voltage supply, this circuit using the process according to the invention and comprising:
passive electrical filtering means in series with the supply source to attenuate the rapid fluctuations of the supply current delivered by said source,
a converter to supply, from the filtered supply source, the phases of the motor, this converter comprising controllable switches having either a passing condition, or a blocked condition, each combination of conditions of said switches defining a conversion configuration:
means to determine the mean supply current of the converter,
means to regulate the supply current arranged to generate, as a function of a current reference and of the current measurement, a regulation logic signal permitting alternating between two couples of configurations of conversion in response to this logic signal, and
a phase sequencer producing reference logic signals which define cycles of magnetization and de-magnetization of the phases, each cycle decomposing into a plurality of periods of sequencing within each of which the reference is sent by the sequencer to the assembly of phases do not change.
According to the invention, this circuit is characterized in that it moreover comprises a selection device disposed between the phase sequencer and the converter and arranged to use, during each period of sequencing defined by the phase sequencer, successively several couples of configurations such that the mean current of the converter respects as closely as possible the reference current.
The phase sequencer produces reference logic signals which define cycles of magnetization and de-magnetization of the phases as a function of the direction of rotation of the motor and of the orientation of the mean mechanical couple desired for the motor.
The selection device is preferably arranged to select the couple of configurations which permits the production of two supply current values straddling as near as possible the current reference and to take into account the magnetization or de-magnetization references of the phases.